The neu gene product is a transmembrane growth-factor-receptor-like tyrosine kinase. It was originally isolated from chemically induced rat neuroblastomas that developed in the offspring of rodents exposed to ethylnitrosourea at a discrete time period of gestation. The chemically induced mutagenic event results in a point mutation (an adenine to thymidine) in the neu gene at the nucleotide level which translates into a single amino acid substitution (valine to glutamic acid) in the neu gene product's transmembrane region. The tyrosine kinase domain of the rat neu gene product becomes constitutively activated by this point mutation in its transmembrane region. The neu gene encodes a 185 Kd surface glycoprotein, termed p185, that possesses tyrosine kinase activity and is structurally similar to the epidermal growth factor receptor (EGFR) at the nucleotide and amino acid level. However, the neu gene has been shown to be distinct from the epidermal growth factor receptor-encoding gene (the c-erb-B gene) by detailed molecular analysis and chromosomal localization studies. The neu gene product's similarity with the epidermal growth factor receptor (EGFR) suggests that p185 is also a growth factor receptor of an as yet unidentified growth modulating factor. The rat and human neu genes are 90% homologous. The relative molecular masses of their protein products differ slightly, Mr=185 kDa for the rat protein and 190 kDa for the human protein. This discrepancy is thought to result from interspecies differences in post-translational modification. See Greene, M. I. et al., "Receptor Systems in Tissues of the Nervous System", Immunological Reviews, Number 100, December 1987 for a review of the neu oncogene, its product and function.
The neu gene and neu gene product refers herein to all mammalian and vertebrate homologies of this gene and its protein product. As used herein, the oncogenic form of the rat neu gene product will be denoted as p185neu. The normal cellular non-oncogenic gene product will be denoted as p185c-neu. The human homologue of the rat neu gene product is referred to herein as c-erb-B-2 or human neu. p185 written alone broadly refers herein to rat and human and other mammalian homologues of the rat neu gene product. p185 involvement in neoplasia and its growth factor receptor like attributes suggest that p185 protein plays an important role in normal and abnormal growth and differentiation of the cells in which it is expressed.
p185 has been found in variety of tissues derived from developing and adult animals in a developmental stage and tissue specific manner, Kokai, Y. et al., (1987) Proc. Natl. Acad. Sci. U.S.A. 84: 8498-8501; Maguire, H. C. et al., (1989) J. Investigative Dermatology 92: 786-790; Cohen, J. A. et al, (1989) Oncogene 4: 81-88. Expression of p185 in the adult rat and human has been detected in the epithelial layers of intestinal villi, basal layer and hair follicles of the skin, pulmonary bronchioles, proximal renal tubules, fallopian tubes, mammary ducts, bladder, and uterine endometrium and in some developing and adult peripheral and central glial cells. Neural and connective tissues express neu during a relatively narrow time window in mid to late gestation, but show no expression in the adult. In secretory epithelial layers of other organs, expression of the neu gene persists into adulthood. Lymphoid tissues do not appear to express the neu gene at any developmental stage.
p185c-neu is expressed on the surface of a number of normal cell types and on the surface of some tumors. Minimal expression of p185c-neu has been found in ependyma, choroid plexus, ciliary body, terminal bronchial epithelium, ovarian stromal epithelium and the loop of Henle. Genitourinary epithelium and normal skin appendages had slightly higher expression. These tissues include bladder transitional epithelium, fallopian tube epithelium, bile duct, collecting duct, endometrial gland epithelium, epidermis, hair follicles, sebaceous gland, and uretheral epithelium. Higher expression of p185 has been found in the rapidly dividing tissues of breast and gastrointestinal tissue. These structures include breast alveolar and ductal epithelium, hepatocytes, proximal and distal tubules, pancreatic islet cells, and gastric mucosa. The highest levels of p185 expression have been found in the rapidly dividing tissues of secretory epithelium and include the meibomian gland of the eye, the cornea, intestinal villus epithelium, pancreatic acinus, pancreatic ductal epithelium, and salivary ductal epithelium. Differential expression of p185 has been found in several types of tissues. In the kidney, the proximal and distal tubules have high expression, whereas there is diminished expression in the Loop of Henle. In the small bowel epithelium, there is minimal expression in the crypts, with gradually increasing expression as the villus tip is reached. In skin, there is minimal expression in the basal layers and increasing expression in the epidermis. There is also staining in the hair follicles.
In human and rat tissues, static tissues and tissues with a slow rate of adult cellular turnover do not express p185. These tissues are of endodermal and mesodermal origin and included lymphoid tissue. Tissues with no expression of p185 include adrenal, blood vessel, brain parenchyma, cartilage, epididymis, heart, lymph node, spleen, striated muscle, testis, thymus, and thyroid.
Although the neu gene has been cloned, identification of the primary ligand for its protein product has been difficult. Though several endogenous p185 modulatory factors may exist, the effect of the primary ligand on p185 should be similar to those of EGF and PDGF on their receptors since these receptors are tyrosine kinases closely related to p185. Yarden, Y., (1988) Annual Review of Biochemistry 57:443; Yarden and Schlessinger,(1987) Biochem. 26:1443; Bishayee, et al., (1989) J. Biol. Chem. 264:11699.
It is an object of the invention to provide substances and methods for altering the cellular metabolism of mammals, particularly humans. It is also an object of the invention to provide substances for treating mammalian tumors, particularly human tumors. Current tumor treatments rely for the most part in the cytotoxic effects of drugs and radiological therapy. Although these treatments bring remission and cure to some patients, they unfortunately have serious side effects because they kill not only tumor cells but also some normal non-tumorous cells. There exists a great need for mammalian tumor treatments which affect primarily the tumor cells, but that have minimal interference with normal cells and cellular functions. It is a further object of the invention to provide methods for diagnosing tumors expressing p185 on the surfaces of the cells. Amplification of human neu gene and subsequent overexpression of the human neu gene product has been implicated in adenocarcinomas in several tissue types including breast, stomach, colorectal, ovary and pancreatic tissue. As a result, c-erbB-2 protein expression levels appear to be a useful prognostic indicator of breast, ovarian and lung cancers. These and other objects will become apparent to persons of ordinary skill in the art from a review of the present specification and the appended claims.